1. Field of the Invention
The present invention generally relates to radio-frequency (RF) circuit modules and radio communication apparatuses, and more particularly, to an RF circuit module and a radio communication apparatus that can be miniaturized.
2. Description of the Related Art
In order to reduce the size of radio communication apparatuses, RF circuit modules in which an RF front end part and a baseband part of a radio communication circuit are modularized have been considered. Such RF circuit modules are designed based on a communication standard, such as Bluetooth™ or a wireless local-area network (LAN), and incorporated into application apparatuses, such as cellular phones or personal computers, to function as modules for providing a radio communication function to the application apparatuses.
From among the RF circuit modules of this type, RF circuit modules in which an RF circuit is integrated with a crystal-oscillator circuit functioning as a reference oscillator of the RF circuit are known. For example, RF circuit modules with the structures described in Japanese Unexamined Patent Application Publication Nos. 10-135756 and 2002-9225 have already been considered.
In addition, for example, a crystal-oscillator circuit described in Japanese Unexamined Patent Application Publication No. 7-99411 is known.
As shown in FIG. 1 of Japanese Unexamined Patent Application Publication No. 10-135756, a structure in which cavities are provided in the front and rear faces of a multilayer substrate, a crystal oscillator and an integrated circuit (IC) are disposed in the cavity in the front face, and a passive component is disposed in the cavity in the rear face is described in Japanese Unexamined Patent Application Publication No. 10-135756. In this structure, since the crystal oscillator and the IC are accommodated in the same cavity, a certain mounting area is required, and it is thus difficult to design a module whose size is close to the chip size of the IC.
As shown in FIG. 1 of Japanese Unexamined Patent Application Publication No. 2002-9225, a structure in which a crystal oscillator, a baseband IC, and a memory IC are disposed on the front face of a multilayer substrate and an RF IC is disposed in a cavity provided in the rear face of the multilayer substrate is described in Japanese Unexamined Patent Application Publication No. 2002-9225. In this structure, since the crystal oscillator and the ICs are disposed on the same face, a certain mounting area is required, as in Japanese Unexamined Patent Application Publication No. 10-135756.
When taking into consideration the fact that single-chip ICs in which an RF circuit block and a baseband circuit block are integrated with each other have been considered and that modules whose size is equivalent to the size of IC chips have been desired in recent years, it is difficult to realize miniaturization with the structures described in Japanese Unexamined Patent Application Publication Nos. 10-135756 and 2002-9225.
As described in Japanese Unexamined Patent Application Publication No. 7-99411, a crystal oscillator circuit includes a crystal oscillator, an inverting amplifier, and a feedback circuit. The crystal oscillator needs to have a mechanical sealing structure, and the inverting amplifier and the feedback circuit are required to be arranged using wiring with the minimum length. Thus, a module structure in which the characteristics of the crystal oscillator circuit can be satisfied and miniaturization can be realized is desired.